青藏高原西北缘晚新生代的隆升特征——来自西昆仑山前盆地的沉积学证据

Late Cenozoic uplift of the northwestern margin of the Qinghai-Tibet Plateau:Sedimentary evidence from piedmont basins of the West Kunlun Mountains.

对西昆仑北缘山前盆地新生代沉积特征的研究结果表明,沿西昆仑山前发育的各沉积序列的垂向特征相似:古新世—中新世早期为石膏层、含瓣腮化石的石灰岩和紫红色较细粒的碎屑岩沉积,指示了海相和海陆过渡相较平静的沉积环境;中新世晚期—上新世初期开始出现陆相磨拉石,指示了陆相非平静的沉积环境,砾石的直径由下至上呈增大趋势,可能反映了西昆仑山体不断隆升,其间相对稳定的层段可能是构造运动间歇期或平稳期的沉积,指示了脉动式的隆升模式;磨拉石底部砾石的成分以沉积岩为主,向上火成岩和变质岩砾石逐渐增多,表明剥蚀程度不断加深。根据磨拉石建造的特征,判断剥蚀量和剥蚀强度自西向东有减小和变弱的趋势,可能暗示了西昆仑山晚新生代隆升有自西向东由强变弱的过渡特征。该结论与本区构造地貌学的研究结果一致。

The study of Late Cenozoic sedimentary characteristics in the piedmont basins on the north margin of the West Kunlun Mountains shows that various sedimentary sequences developed along the piedmont of the West Kunlun Mountains have similar characteristics in vertical sections. Paleogene deposits consist of gypsum beds, limestone containing lamellibranches and purplish red fine clastic rocks, indicating a quiet marine and paralic sedimentary environment. Continental molasses started deposition from the latest Miocene-earliest Pliocene, indicating an unquiet continental sedimentary environment. The tendency of coarsening-upward of gravels may indicate the accelerated uplift of the West Kunlun. The intervals of almost invariable gravel diameters may mark the intermittency of tectonic movement or stable deposition, indicating a pulsating uplift model. The molasses are mainly composed of sedimentary rocks at the bottom and igneous rocks and metamorphic rocks at the top, indicating acceleration of denudation. According to the features of the molasses, both the volume and intensity of denudation have a tendency of decreasing and weakening from west to east, implying easterly weakening of the tectonic uplift of the West Kunlun during the Late Cenozoic. The conclusion also coincides with the result of morphotectonic research in the area.